Conventionally, plaster bandages made by impregnating coarse gauze with plaster of Paris have been used to immobilize body members, but this has many disadvantages, including that the plaster bandages contaminate the surrounding area by dropping plaster of Paris during treatments, and is heavy for patients and poor in permeability. Also the moisture used during curing does not evaporate for two to three days, keeping the affected portion wet for many hours, and after curing, the strength deteriorates when it makes contact with moisture. In addition, the plaster bandages absorb and disperse X-rays, preventing accurate X-ray diagnosis of the affected portion.
To replace the plaster bandage, there has been proposed a casting tape comprising a fibrous substrate which is knitted with glass fiber in tapes and coated with polyurethane resin which is wrapped around the affected portion and cured through reaction of polyurethane resin with moisture. The orthopedic casting tape using this water-curing resin has various advantages over the plaster bandage using plaster of Paris, including that it is light-weight, has good permeability, its strength does not deteriorate once it cures, and it permits better X-ray penetration.
For the fibrous substrate used in the orthopedic casting tape using a water-curing resin, nonwoven fabric, woven fabric, and knitted fabric comprising glass fiber, cotton, polyester, acrylic, polyethylene, nylon, and other materials in different forms, weight per unit area, and knitting methods have been disclosed such as in USP 4,502,479 USP 4,376,438, USP 4,652,493, USP 4,572,171, USP 4,427,002, and Japanese Unexamined Patent Application Publication No. 59-6060 (1984), among which glass fiber is particularly popular. The glass fiber is advantageous in holding strength, but has a disadvantage of poor conformability (modeling) because of its rigidity and nonstretchability. Therefore, U.S. Pat. No. 4,609,578 by Reed discloses that introduction of the knitted fabric used decreases this disadvantage by pleating or folding back the bandage when it is wrapped around the body profiles, such as around heels and elbows. U.S. Pat. No. 4,683,877 by Ersfeld et al proposes an orthopedic plaster bandage, but it is still insufficient to completely conform the fiber glass plaster bandages to the complicated curves and protrusions of a body member.
As a proposal to positively solve this problem a casting tape incorporating high modulus fibers and an elastomeric fiber has been recently announced, i.e. U.S. Pat. No. 4,668,563 of Buese and Yoon. For the high modulus fiber, glass fiber is used, and for an elastomeric fiber, natural rubber is used. Maintaining the strength with glass fiber and providing greater lengthwise extensibility with natural rubber improves the problems when the fibrous substrate comprises solely glass fiber. Any desired elasticity can be obtained by selecting the thickness and density of rubber yarns because an elastomeric fiber is used. However, with the elastomeric fiber the recovery force (force of the fiber to return to the original position when elastic goods are stretched) increases proportional to the stretching force imposed, and moreover, at the protusions or body sections where the number of bandage wraps is increased to protect and immobilize the affected portion, the recovery force is increased double to triple. Therefore, when such casting tape is applied to protrusions (in particular, edema) or lower legs with many protrusions and curves, the casting tape must be applied while stretched in order to achieve good comformability, and many wraps must be installed around articulations of feet and knees to secure proper strength, preventing the casting tape from wrapping with uniform adherence. In addition, the casting tape requires 10 minutes for apparent curing and about 30 minutes for complete curing, gradually constricting the affected portion by the recovery force during this curing time, and there is a danger of causing circulation trouble, eventually resulting in decubitus ulcers or necrosis. In addition, when glass fiber is used for the high modulus fiber, conformability to the affected portion is still not satisfactory, as discussed above. In addition, the casting tape using rubber as the elastomeric fiber tends to cure urethahe prepolymer resin earlier than intended, thus shortening the shelf life of casting tape. When using rubber as the elastomeric fiber, treatments such as solvent treatment, drying, acid treatment, and rinsing and drying are required, resulting in complexity in the manufacturing process. When using polyurethane synthetic fiber, urethane prepolmer swells the elastic yarn of polyurethane synthetic fiber, tending to degrade elasticity and requiring special processing of the fiber. Also an additional problem occurs in that the elastomeric fiber makes it difficult to cut the once-cured casting tape with a plaster bandage cutter.
The objects of the present invention are to obtain an orthopedic casting tape that is free from defects as described above of conventional casting tapes, that is, poor comformability to the affected portion, short shelf life, complicated manufacturing process, and difficultly in cutting.